This invention pertains to compatible low shrink resin systems.
In one of its more specific aspects, this invention pertains to low profile, low shrink resin systems employable in the production of fiber-reinforced molded parts, the resin system being a homogenous, one-part system comprising a thermoplastic resin and a thermosetting resin.
The use of resin systems which comprise a combination of thermoplastic and thermosetting polymers, the combination producing low sink and low shrink molded parts, is well known. Generally, such systems comprise a thermosetting resin, that is, an unsaturated polyester, a thermoplastic resin and a monomer which cross-links with the polyester. Such systems usually contain other ingredients such as catalysts, glass fibers, fillers, pigments, mold-release agents and the like.
These systems form the basis for sheet and bulk molding compounds which, when molded, form comparatively light-weight durable articles of superior surface characteristics.
Such resin systems are described and claimed in U.S. Pat. No. 3,772,241 to C. H. Kroekel. However, the resin systems described therein exist, prior to incorporation into molding compounds, as two-part systems; that is, they are systems in which the thermoplastic resin and the polyester-monomer combination are incompatible and after being mixed, separate on standing to form two phases.
The disadvantages of such systems include the need for individual storage systems for each resin, the need to mix only at the time of use and the need to use soon after mixing and prior to the separation.
While one-phase polyester-thermoplastic resins do exist as described, for example, in U.S. Pat. Nos. 4,035,439 and 3,883,612, the systems are limited to rather specific components as the elements of the combination resin system.
There has now been discovered a resin system embodying a wider range of components which system is not subject to phase separation under prolonged periods of standing.